The present invention involves a video camera control system for providing a plurality of control signals for selectively enabling a corresponding plurality of control functions in a video camera.
In the majority of the known control systems, where it is desired to selectively control a plurality of different functions, it is necessary that a different switch be included in the input circuit of the system for providing an appropriate signal for controlling each of these functions. Each of the signals is then coupled by a separate transmission line from the input circuit to the actual control circuit for activating the corresponding function. Representative embodiments of such systems are disclosed in U.S. Pat. Nos. 3,312,941 to Booth et al; 3,508,201 to Morale; 3,688,262 to Liquori and 3,719,828 to Lipskin. Since in each of these devices, there is almost an exact correspondence between the number of input selection members and the number of output functions that can be controlled by the system, there is a direct linear relationship between the control capability of the system and the size of the input device. Thus, as the intended use of the system expands, the size and cost of the control system expands at the same rate. Furthermore, since in each of these systems there is almost always a direct link, i.e., transmission line, between each of the input selecting members and the control circuit, it is difficult to separate the input circuit and the control circuit by any significant distance unless one is willing to utilize a large amount of wiring between the circuits.
The patent to Liquori is possibly of particular interest since the embodiment disclosed by this patent was designed for controlling a plurality of audio-visual devices, which is likewise an area in which the control system of the present invention can be of particular utility. In the system disclosed by the patent to Liquori each of the input buttons is directly connected by a separate line to a remote control assembly, which assembly provides an appropriate output signal that is supplied to each of the audio-visual devices to be controlled.
While several attempts have been made to limit the number of input selecting members which must be utilized in order to control a plurality of control functions, these systems have generally encountered problems of either simultaneously activating a plurality of control functions or entailing such a cumbersome method for avoiding such simultaneous activation that the system becomes impractical. Examples of such systems are disclosed in U.S. Pat. Nos. 3,050,713 to Harmon and 3,569,741 to Bolick et al.
The patent to Harmon discloses a circuit having a plurality of thyratrons that are selectively activated based upon the level of the signal supplied to a signal source. Each of the thyratrons is activated only when an applied input signal is above a corresponding predetermined level. When the thyratron is activated, it generates an output signal for enabling a corresponding control function. Thus, for each control function to be activated by the control circuit, it is necessary to have a separate thyratron. In order to prevent simultaneous actuation of more than one thyratron at a time, a plurality of delay circuits is employed. These delay circuits are coupled with the thyratron such that the thyratron which is activated by the lowest level signal is not activated until the longest delay period has passed. Thus the higher the level of the signal, the shorter the time period that signal is applied while conversely the lower the level, the longer the time period the signal is applied. The duration of the applied signals are selected so as to correspond with the delay circuits coupled to the thyratrons so that the signal only exists long enough to activate the appropriate thyratron.
The patent to Bolick et al discloses a control circuit for selectively activating different operations within a recording device. The circuit includes a plurality of transistors, each of which is activated when the voltage applied to its base is above a predetermined level. In the system disclosed by this patent, if the level of the applied voltage is sufficient to activate the third level transistor, then the first and second level transistors will be simultaneously actuated.
One other control circuit which has been developed in the prior art is that shown in U.S. Pat. No. 3,670,180 to Grossimon et al. In contrast to the systems disclosed in the other patents, however, in accordance with the embodiment disclosed by this patent a plurality of SCRs are sequentially activated by a series of input signals. The values of the input signals sequentially increase and each of the signals serve to actuate a corresponding SCR. The purpose of the control system disclosed by this patent is to fire a series of rockets in a predetermined order and thus the SCRs need only be actuated in accordance with this predetermined order and it is impossible to selectively actuate the SCRs in any other order.
All the systems disclosed by the patents discussed above involve extremely sophisticated and cumbersome circuitry for carrying out a plurality of control functions. If only a relatively few functions are to be controlled by the system, the utilization of separate circuits for each function may not present a significant burden. As the number of functions to be controlled grows, however, the size of the system grows at the same rate thereby increasing the complexity and cost of the system.
Considering the references cited in applicant's copending U.S. Patent Application cited above, U.S. Pat. No. 3,932,714 to Guimier et al discloses a remote electrical transmission system in which a control unit provides a different level voltage output, in dependence upon the position of a selector switch, to a receiver unit including a plurality of zener diodes and associated switching transistors which open or close different control circuits according to the positions in which the control selector switch is set. U.S. Pat. No. 4,028,620 to Kitagawa et al discloses a system for selectively actuating electrical loads including an instruction unit having a switch mechanism with a plurality of contacts, and an output unit for generating respective output signals corresponding to the voltage signals from the instruction unit. U.S. Pat. No. 4,070,650 to Ohashi et al discloses a digital signal transmission system in which control signals are either transmitted or not transmitted in accordance with the results of a comparison between set values stored in a decoder and digital signals transmitted from an encoder. When the values of the digital signals are greater than the value set in the decoder comparators output signals are generated. The output signals are suspended if the values of the digital signals are smaller than those set in the decoder comparators. Clearly, none of these references disclose or suggest the advantageous arrangement of switch devices and associated blocking devices employed in the present invention to control the functions of a video camera system.